Among the known methods of polymerization grafting of ethylenically unsaturated monomers onto elastomer skeletons which can be grafted, the so called "aqueous emulsion method" is satisfactory only in the case in which the latexes used for grafting are polydispersed. When this same procedure is applied to monodimensional elastomer latexes, products are obtained whose hot fluidity (flow) and surface appearance may be satisfactory, but whose shock resistance is mediocre. Other known methods described, in particular in U.S. Pat. Nos. 3,370,105 and 3,436,440 and in French Pat. Nos. 2,233,365 and 2,304,645, consist in placing graftable elastomer latexes into suspension. These known methods make it possible to obtain products whose shock resistance is high and whose hot fluidity (flow) can likewise be good, but whose hardness and tensile strength are low and, above all, whose surface appearance is mediocre. It has heretofore not been possible to obtain graft polymers whose mechanical properties and surface properties are entirely satisfactory.